Strange Vibration, Does this sound plausible?
07-28-2008, 10:19 PM
#1
Strange Vibration, Does this sound plausible? I recently installed some UMI Bolt-On LCA Relocation brackets. I LOVE the added hook they gave me. Since I put them on, however, there's a weird vibration at 60mph+. I've dealt with and solved vibrations before, but this one I can't quite nail down. I do have a few ideas though.
First off, a little about the car.
-3350 lbs, SI Stalled A4, Stock 10 bolt
-Poly Motor Mounts, Poly ES Trans Mount, UMI TA Relocation Bracket, Factory TA
-BMR non-adj LCA's, UMI LCA Relo Brackets (bottom hole), BMR non-adj PHR
-Aluminum DS, One Coil cut out of Front Springs, "Hose Mod" rear springs
I think that covers most of what we need to know.
First off, the vibration is cyclical. It will ramp up, ramp down, then stop. It will do this over and over again within the span of a few seconds. The vibration seems worse when changing lanes or turning.
Checked pinion angle today, and it's either -1 or -2 depending on where you measure from. Driveshaft yoke is properly in the transmission. The front yoke seems to be *slightly* ( I mean, I might be imagining it ) crooked in the tailshaft. No binding or anything in the driveline though.
Here are my ideas.
-Un-centered rear axle, I quick-checked this earlier with a sheet of paper, and the axle seems to be about 1/2 closer to the driver's side. I'll be using the plumb-bob method to properly check this tomorrow, and will post back up.
-Axle not centered in wheel wells. I tried to raise the LCA's back up one hole today, and they didn't really want to move, as if they were binding because they weren't straight in the bracket. Will measure tomorrow and post back up.
-Bent driveshaft or slung driveshaft weight. Inspected today, and I don't think that's it.
Any ideas or suggestions what else to look for would be appreciated.
Thanks,
Allen
First off, a little about the car.
-3350 lbs, SI Stalled A4, Stock 10 bolt
-Poly Motor Mounts, Poly ES Trans Mount, UMI TA Relocation Bracket, Factory TA
-BMR non-adj LCA's, UMI LCA Relo Brackets (bottom hole), BMR non-adj PHR
-Aluminum DS, One Coil cut out of Front Springs, "Hose Mod" rear springs
I think that covers most of what we need to know.
First off, the vibration is cyclical. It will ramp up, ramp down, then stop. It will do this over and over again within the span of a few seconds. The vibration seems worse when changing lanes or turning.
Checked pinion angle today, and it's either -1 or -2 depending on where you measure from. Driveshaft yoke is properly in the transmission. The front yoke seems to be *slightly* ( I mean, I might be imagining it ) crooked in the tailshaft. No binding or anything in the driveline though.
Here are my ideas.
-Un-centered rear axle, I quick-checked this earlier with a sheet of paper, and the axle seems to be about 1/2 closer to the driver's side. I'll be using the plumb-bob method to properly check this tomorrow, and will post back up.
-Axle not centered in wheel wells. I tried to raise the LCA's back up one hole today, and they didn't really want to move, as if they were binding because they weren't straight in the bracket. Will measure tomorrow and post back up.
-Bent driveshaft or slung driveshaft weight. Inspected today, and I don't think that's it.
Any ideas or suggestions what else to look for would be appreciated.
Thanks,
Allen
07-29-2008, 07:46 AM
#2
My first guess...
Is the transmission poly mount... try removing it and replacing it with a stock one to eliminate it as a issue.. it could be the problem.
On the relocation kit from us.. does it have the multiple instant center holes where you mount the torque arm? If so since you have a factory torque arm make sure it is mounted in the second set of holes from the top.
Hope that helps,
Ryan
Is the transmission poly mount... try removing it and replacing it with a stock one to eliminate it as a issue.. it could be the problem.
On the relocation kit from us.. does it have the multiple instant center holes where you mount the torque arm? If so since you have a factory torque arm make sure it is mounted in the second set of holes from the top.
Hope that helps,
Ryan
07-29-2008, 07:24 PM
#4
Well, on your suggestions, I removed the trans-mount today and shaved the bumps. I'm not going back with a stock rubber, I broke them all the time.
I did notice something interesting. When I installed the Relo Bracket, the bolt for the mount *barely* made it back in, I'm talking I had to thread it first, then force the crossmember into place, the bolt was all the way to the back of the hole.
When I reinstalled the mount today, the bolt went back in the CENTER of the hole, so I'm thinking that something was in a bind somewhere on the tranny. In any case, on the ride home tonight, the vibration was all but gone at speeds below 70, and cruising at 70 and above, was greatly reduced, but still there. Ryan, what torque does the trans mount bolt need to be at with your crossmember? I couldn't remember today, so I torqued it to 50ft/lbs.
The rear axle wasn't any more than 1/4" off front to back, and less than 1/8" off side-to-side, so I figure that it's centered well enough.
Oh, and to answer your question Ryan, yes it's in the 2nd hole down. I figured that out when I installed it.
I did notice something interesting. When I installed the Relo Bracket, the bolt for the mount *barely* made it back in, I'm talking I had to thread it first, then force the crossmember into place, the bolt was all the way to the back of the hole.
When I reinstalled the mount today, the bolt went back in the CENTER of the hole, so I'm thinking that something was in a bind somewhere on the tranny. In any case, on the ride home tonight, the vibration was all but gone at speeds below 70, and cruising at 70 and above, was greatly reduced, but still there. Ryan, what torque does the trans mount bolt need to be at with your crossmember? I couldn't remember today, so I torqued it to 50ft/lbs.
The rear axle wasn't any more than 1/4" off front to back, and less than 1/8" off side-to-side, so I figure that it's centered well enough.
Oh, and to answer your question Ryan, yes it's in the 2nd hole down. I figured that out when I installed it.
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10-05-2008, 09:56 PM
#8
UPDATE:
Vibration came back, so I went searching for it again and FOUND IT! The car is doing much better so far.
It was the tailshaft housing bushing. It was allowing the front drive yoke to vibrate. Funny thing was, it only measured .015 bigger than the OD of the yoke. I could move the driveshaft up and down pretty good though, about a 1/8th of an inch. Replaced it with one that only had about .001 clearance bigger than the yoke and it's fine now. I had to wallop the shaft in with a rubber mallet, but it went in.
Just thought I'd update this for anyone trying to chase down a vibration.
Vibration came back, so I went searching for it again and FOUND IT! The car is doing much better so far.
It was the tailshaft housing bushing. It was allowing the front drive yoke to vibrate. Funny thing was, it only measured .015 bigger than the OD of the yoke. I could move the driveshaft up and down pretty good though, about a 1/8th of an inch. Replaced it with one that only had about .001 clearance bigger than the yoke and it's fine now. I had to wallop the shaft in with a rubber mallet, but it went in.
Just thought I'd update this for anyone trying to chase down a vibration.